He has a exactly right. If your looking for more compression mill your head. Cant change domes you say? Buy like 4 stock heads and mill them...still cheaper than a cool head and all of those domes. I have a digital temp gauge and the only thing that actually dropped the temp was engine ice, by about 8 degrees, pretty impressive. I do have a billet impeller, I really dont see how that would make a difference but I guess I cant call coolheads total BS until I test it on a stock impeller. Maybe the billet impeller is creating such a greater flow, it neutralizes the cool head? Doubt it. Plus o-rings are like $20 bucks.